<!DOCTYPE HTML>

<html>
<head>
<title>OffscreenCanvas with style resize: green rectangle with yellow borderon white background.</title>
<style type="text/css">
.nomargin {
  margin: 0px auto;
}
</style>
<script>
var g_swapsBeforeAck = 15;

function main()
{
  var canvas = document.getElementById("c");
  window.requestAnimationFrame(function() {
    canvas.style.width = '100px';
    canvas.style.height = '200px';
    canvas.style.border = '10px solid yellow';
    window.requestAnimationFrame(function() {
      var offscreenCanvas = canvas.transferControlToOffscreen();
      drawTriangle(offscreenCanvas);
    });
  });
  waitForFinish();
}

function drawTriangle(canvas)
{
  var gl = canvas.getContext("webgl");
  gl.clearColor(0, 1, 0, 1);
  gl.clear(gl.COLOR_BUFFER_BIT);

  var prog = gl.createProgram();
  var vs = gl.createShader(gl.VERTEX_SHADER);
  gl.shaderSource(vs, ['attribute vec2 pos;',
      'void main() {',
      '  gl_Position = vec4(pos, 0., 1.);',
      '}'].join('\n'));
  gl.compileShader(vs);
  if (!gl.getShaderParameter(vs, gl.COMPILE_STATUS)) {
      throw 'failed to compiled shader';
  }
  gl.attachShader(prog, vs);

  var fs = gl.createShader(gl.FRAGMENT_SHADER);
  gl.shaderSource(fs, ['void main() {',
      '  gl_FragColor = vec4(1.);',
      '}'].join('\n'));
  gl.compileShader(fs);
  if (!gl.getShaderParameter(fs, gl.COMPILE_STATUS)) {
      throw 'failed to compiled shader';
  }
  gl.attachShader(prog, fs);

  gl.linkProgram(prog);
  if (!gl.getProgramParameter(prog, gl.LINK_STATUS)) {
      throw "Could not link the shader program!";
  }
  gl.useProgram(prog);

  gl.bindBuffer(gl.ARRAY_BUFFER, gl.createBuffer());
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-.5,0, 0,.5, .5,0]), gl.STATIC_DRAW);
  var attr = gl.getAttribLocation(prog, 'pos');
  gl.enableVertexAttribArray(attr);
  gl.vertexAttribPointer(attr, 2, gl.FLOAT, false, 0, 0);

  gl.drawArrays(gl.TRIANGLE_STRIP, 0, 3);
}

function waitForFinish()
{
  if (g_swapsBeforeAck == 0) {
    domAutomationController.send("SUCCESS");
  } else {
    g_swapsBeforeAck--;
    document.getElementById('container').style.zIndex = g_swapsBeforeAck + 1;
    window.requestAnimationFrame(waitForFinish);
  }
}
</script>
</head>
<body onload="main()">
<div style="position:relative; width:300px; height:300px; background-color:white">
</div>
<div id="container" style="position:absolute; top:0px; left:0px">
<canvas id="c" width="300" height="300" class="nomargin"></canvas>
</div>
</body>
</html>
